Multiple-nip calender and calendering arrangement

ABSTRACT

A supercalender for calendering a paper web and a calendering arrangement for producing matte-quality paper web has a multiple-nip calender in which at least one of the calendering nips of the multiple-nip calender is an extended nip (N 9 ) formed between a polymer roll ( 18 ) and either a shoe roll ( 30 ) or a calendering belt.

CROSS REFERENCES TO RELATED APPLICATIONS

This application is a U.S. national stage application of InternationalApplication No. PCT/FI01/00284, filed Mar. 21, 2001, and claims priorityon Finnish Application No. 20000671, filed Mar. 22, 2000, thedisclosures of both of which applications are incorporated by referenceherein.

STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSOREDRESEARCH AND DEVELOPMENT

Not applicable.

BACKGROUND OF THE INVENTION

The present invention relates to a multiple-nip calender, such as asupercalender, for producing a matte-quality paper web, said calendercomprising a roll system composed of a plurality of rolls arranged to bein nip contact with each other or a corresponding roll stack, in which apaper web to calender the same is arranged to pass through the nips.

The roll system of a conventional supercalender comprises a number ofrolls, usually eight to fourteen rolls, arranged into a superimposedroll stack. The superimposed rolls are in nip contact with each otherand the paper web to be calendered is arranged to run through the nipsbetween the rolls. Also, such supercalenders are known in the art inwhich the rolls of the roll system are so arranged that the nip levelmainly common to the roll nips is arranged to be essentially horizontalinstead of using a vertical roll stack. As regards the calenderingresult, it is not, however, of great importance whether a vertical orhorizontal roll system is used. A highly conventional supercalenderdesign is disclosed in, for example, Fl patent specification No. 81 633.

When wishing to raise the level of calendering with currently knowndesigns, the sole possibility is, in fact, to increase the number ofcalendering nips in the supercalenders. This leads to a more complicatedcalender structure and to a more difficult control and tail threading ofthe paper web. Especially when on-line machines are in question,conflicts may be caused by the great running speed and full-speed tailthreading. Endeavours have been made to solve the problems by, forexample, different belt and shoe calenders, with which the calenderingnip is extended and, therethrough, the activity of the nip isintensified. As to the state of art related to belt calenders, referenceis made, for instance, to Finnish patent specifications Nos. 95 061, 102304, and 102 305. As regards the state of the art related to shoecalenders, reference is made further to German application specificationNo. 43 44 165 and U.S. Pat. No. 5,163,364.

Using belt calenders and shoe calenders, a gloss corresponding to asupercalendered quality or fairly close to the gloss achieved bysupercalendering is achieved, though achieving an equivalent smoothnessis difficult. In order to avoid one-sidedness problems of the calenderedpaper, it is in general indispensable to use at least two extended nipsprovided with a belt or a shoe roll. In a belt and shoe calender nip,the maximum pressure will be lower thanks to the wider nip than inconventional nips formed between two rolls, because of which the beltand shoe calenders are best appropriate for paper grades in which themaintaining of bulk is of a great importance. They are thought to beparticularly well appropriate for use in calendering cardboard.

According to the prior art, when calendering a paper web to achieve amatte-quality paper web, the calendering nip is formed between a polymerroll and a specially coated, heatable thermoroll or between two polymerrolls. The problem is now especially the short nip area in the runningdirection of the web involving detrimental resulting effects causedthereby in producing a matte-quality paper web.

SUMMARY OF THE INVENTION

A first objective of the present invention is to provide a novelsolution in a multiple-nip calender, by which solution are provided as acombination those advantages which are related to current multiple-nipcalenders and to e.g. belt and shoe calenders provided with an extendednip.

A second objective of the present invention is to provide a novelcalendering arrangement for forming a calendering nip in order to makefeasible production of matte-quality, that is, non-gloss and smoothpaper web easier than before, especially a more easily controllablecalendering when producing matte-quality paper web.

To achieve the objects of the invention, the multiple-nip calender ofthe invention mentioned at the beginning is mainly characterized in thatat least the first and/or the last calendering nip of the multiple-nipcalender is an extended nip.

With the present invention, a plurality of advantages are gained knownin prior art technology, and for instance the following of saidadvantages may be introduced in the present context. In the inventionthe properties of an extended nip and a conventional supercalender arecombined, whereby, especially when using an extended and low-pressurenip as the first nip of the calender, paper can be heated, plasticizedand worked appropriately with this kind of extended and low-pressure nipprior to the actual nips of the supercalender. In this manner, the bulkof the paper can be saved without compromising over otherquality-related characteristics. With the aid of the invention, thequality properties of superior paper are achieved in one and the samepaper density. With an extended nip connected to the supercalender, thepaper gloss is increased by reducing the microroughness. The gloss andsmoothness of the paper are in general superior to conventional designsand the uniformity of pressed gloss is better than earlier. Thecalendering process is in general a highly “violent” measure consideringthe paper, but especially when a nip extended in the manner disclosed inthe invention is used as a first nip of the supercalender, it will notcause stress to the paper to the extent the conventional nips do,whereby the structure of the paper will not suffer in the calendering.The strength properties of the paper remain good. With the design of theinvention, more surface-directional forces are achieved and, on thestrength of said surface-directional forces and plasticizing of the web,the smoothness of the paper to be calendered also exceeds theconventional level.

Of the advantages of the invention related to producing a matte-qualitypaper web, one may mention that an extended nip and, as a result ofcalendering, an excellent and non-gloss microsmoothness of the surfaceare achieved. However, the quality of the calendering result is limitedin that if so-called Bendsen smoothness is desired, other calenderingdesigns have to be used.

The other advantages and characteristic features of the invention becomeobvious in the following detailed description of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described below in an exemplary fashion, referencebeing made to the figures of the accompanying drawings.

FIGS. 1A, 1B and 1C present various embodiments of the invention, inwhich in a multiple-nip calender such as a supercalender, at least oneextended nip is arranged with the aid of an extended nip roll.

FIGS. 2A, 2B and 2C present various embodiments of the invention, inwhich in a multiple-nip calender such as a supercalender, at least oneextended nip is arranged with the aid of a belt device including acalendering belt.

FIG. 3 presents an advantageous embodiment for producing a matte-qualitypaper web.

FIG. 4 presents a second advantageous embodiment for producing amatte-quality paper web.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1A is a completely schematic and principle presentation of asupercalender comprising a roll stack 10A composed of rolls arranged tobe superimposed, in which the rolls of the roll stack form calenderingnips N₁-N₉ therebetween, wherethrough a paper web W to be calendered isarranged to pass. In the presentation of FIG. 1A, a first nip N₁ of thesupercalender is an extended nip formed between an extended nip roll 20and a first intermediate roll 11 of the calender. In the presentembodiment, the extended nip roll is advantageously a SymBelt™ roll.Said extended nip roll comprises a roll support 21, whereupon a flexibleroll shell 22 is arranged to rotate, a so-called hose shell. Towards thenip N₁, the hose shell 22 is pressed with the aid of a formedcompression shoe 23. A paper web W to be calendered is conducted to thefirst nip N₁ with the aid of a guide roll 41 and it is taken off fromthe nip by means of a pull-out roll 42 so that the paper web is releasedfrom the surface of the first intermediate roll 11. Respectively, aftereach nip the paper web is released from the surface of the calender rollwith a pull-out roll 42, 43, 44, 45, 46, 47, 48, 49, and respectively,it is conducted from the pull-out roll to a subsequent nip. From thelast nip N₉, being in FIG. 1A formed between the last intermediate roll18 and the lower roll 35 of the supercalender, the paper web W isconducted for instance to a reeler.

FIG. 1B presents a principle image of a second embodiment of theinvention, in which the roll stack of the supercalender is indicated byreference 10B. In the parts in which FIG. 1B is equivalent to FIG. 1A,the same references are used. In the embodiment of FIG. 1B, a first nipN₁, of the supercalender is a conventional roll nip formed between anupper roll 25 and a first intermediate roll 11 of the supercalender. Insaid embodiment, the last nip N₉ of the calender is an extended nipformed between the last intermediate roll 18 and the extended nip roll30 used as the bottom roll. The extended nip roll is advantagoeusly aSymBelt™ roll. Thus, the extended nip roll 30 is equivalent in structureto the extended nip roll 20 presented in FIG. 2A in that the roll 30comprises a roll support 31, on which a flexible roll shell is arrangedto be rotating, a so-called “hose shell”. The hose shell 32 iscompressed against the last intermediate roll 18 with the aid of aformed press shoe 33 for forming the extended nip N₉. The web is takenout from said last nip N₉ with the aid of a guide roll 50.

FIG. 1C presents one more principle embodiment of the design of theinvention. In FIG. 1C, the roll stack of the calender is denoted withreference 10C and the same reference numerals are used in FIG. 1C as inthe parts in common in FIGS. 1A and 1C. The principle presentation ofFIG. 1C is in a way a combination of the designs shown in FIGS. 1A and1B in that in the present example both the first nip N₁ and the last nipN₉ of the supercalender are extended nips. Said extended nips N₁, N₉ areformed in a manner similar to those described in association with FIGS.1A and 1B, in this aspect, reference is made to the description of FIGS.1A and 1B.

FIG. 2A presents one more alternative embodiment of the design of theinvention. In said presentation of FIG. 2A, being a completely principleimage of the supercalender, the roll stack of the calender is markedwith reference 110A. The presentation of FIG. 2A is to a large extentequivalent to the embodiment shown in FIG. 1A in that also in thepresentation of FIG. 2A the first nip N₁ of the calender is formed intoan extended nip. Said extended nip N₁ is provided with the aid of a beltdevice 122, 123, said belt device comprising a calender roll 121, aroundwhich a calendering belt 123 is conveyed, said belt being formed into anendless link and supported with the aid of guide rolls 122. Thus, thecalendering belt 123 passes from the extended nip N₁ between thecalender roll 121 and the first intermediate roll 111. The intermediaterolls of the calender are therefore indicated by reference numerals 111,112, 113, 114, 115, and 116. As in the presentation of FIG. 2A, thepaper web W is conducted to the first calendering nip N₁, from which itis taken out with the aid of a pull-out roll 141 and conducted to asubsequent calendering nip N₂, from which it is taken out with the aidof a subsequent pull-out roll, etc. So, the pull-out rolls are markedwith reference numerals 141, 142, 143, 144, 145, and 146. Finally, thepaper web is conducted to the last calendering nip N₇ formed between thelast intermediate roll 116 and the lower roll 135 of the calender. Fromsaid last calendering nip, the paper web is guided e.g. to a reeler.

The embodiment of FIG. 2B is to a large extent equivalent to that shownin FIG. 1B in that the first nip N₁ of the calender also in FIG. 2B is aconventional roll nip formed between an upper roll 125 of the calenderand a first intermediate roll 111. In the present embodiment, the lastnip N₇ of the calender is, instead, an extended nip formed between alast intermediate roll 116 of the calender and the belt device 130. Thebelt device 130 in turn is equivalent to the belt device 122, 123 as inFIG. 2A in that the belt device 130 comprises a calender roll that isequivalent to calender roll 131 of FIG. 2C and wherearound a calenderingbelt 133 formed into an endless link is conveyed, said calendering beltbeing supported with the aid of guide rolls 132. In the presentation ofFIG. 2B, the paper web passes in the manner equivalent to FIG. 2Abetween the nips N₁ through N₇ of the calender so that from the nip N₆before the last nip of the calender the paper web is conducted with theaid of pull-out rolls 147 and 148 into an extended nip N₇ between thebelt device 130 and the last intermediate roll 116. The roll stack ofthe calender is denoted with reference 110B. In other respects, thecalender of said embodiment is equivalent to that shown in FIG. 2A andtherefore, the equivalent parts are referred to by same referencenumerals. In this respect, reference is thus made to the description ofFIG. 2A.

FIG. 2C presents further an additional embodiment of the design of theinvention and the calender presented in FIG. 2C is in a way acombination of the calenders of FIGS. 2A and 2B in that both the firstnip N₁ and the last nip₇ of the calender of FIG. 2C are extended nips.Said extended nips N₁ and N₇ are formed with the aid of belt devices122, 123 and 130 in the manner shown in FIGS. 2A and 2B. The roll stackof the calender is indicated by references 110C in FIG. 2C. In otherrespects, the embodiment of FIG. 2C is equivalent to that shown in FIGS.2A and 2B and therefore, reference in the present context is made to thedescription of FIGS. 2A and 2B.

FIG. 3 presents a one-nip calender of an advantageous embodiment of theinvention for coating a matte-quality paper web. A paper web W to becalendered is conducted in the direction shown by an arrow into acalendering nip N, which is an extended nip, formed between a rotatingpolymer roll 18 and a thin-shelled, flexible shoe roll 30 rotating abouta fixed axial body. The shoe roll 30 is preferably an extended nip rollmarketed by Metso Paper, Inc. under the trademark SymBelt™. The flexibleshell of the shoe roll 30 is loaded by a radially inside formed loadingshoe 33 disposed onto the axial body to be radially movable, with theaid of which the flexible shell 32 of the shoe roll 30 is pressedagainst the shoe roll 18. Thus, the polymer roll 18 acts as a stop rollto the shoe roll 30 for forming a calendering nip N.

FIG. 4 presents a multiple-nip calender of a second advantageousembodiment of the invention for coating matte-quality paper web. Thepaper web W to be calendered enters in the direction of an arrow intothe calendering nip N, which is an extended nip and which in theembodiment of the figure is formed against the upper roll 11 and thebottom roll 18 of the calender. An advantagoues multiple-nip calenderappropriate in the connection with the invention is the multiple-nipcalender marketed by Metso Paper, Inc. under the trademark Optiload™.Both the upper roll and the bottom roll are polymer rolls and in saidsecond embodiment of the invention, the calendering nip N is formedbetween a flexible calendering belt 133, arranged to be pressed againstthe polymer roll 11 and 18 with the aid of tension devices. Thus, thepolymer roll 11 and 18 serves also in the calendering arrangement of thepresent embodiment as a stop roll for forming a calendering nip N. Ascan be seen in the figure, for the tension devices of the calenderingbelt 133, a first, second, third and fourth guide roll 132 are used inthe second embodiment of the invention, around which the endlesscalendering belt 133 passes. One of the guide rolls, the first top leftguide roll 132 in the nip N against the bottom roll 18 and the guideroll 132 down on the left in the nip N against the upper roll 11, can bepositioned in vertical direction, whereby the tension of the calenderingbelt 3 and pressing against the polymer roll 11 or 18 acting as the stoproll as well as the length of the calendering nip N can be adjusted.

As advantageous embodiments of the invention a one-nip calender may befurthermore mentioned, whereby the calendering nip of the inventionhaving the capacity to produce matte quality is the only nip of thecalender, and a multiple-nip calender, whereby advantageous targets forapplication is the forming of a calendering nip of the inventionproducing matte quality against the upper roll of a multiple-nipcalender or against a bottom roll of a multiple-nip calender.

The invention is described in the foregoing in exemplary fashion,referring to the figures of the accompanying drawing. However, theinvention is not restricted to concern solely to the examples associatedwith supercalenders presented in the figures, instead, variousembodiments of the invention may, related to various multiple-nipcalendars, be varied within the inventive idea determined in theaccompanying claims.

What is claimed is:
 1. A multiple-nip calender, for producing amatte-quality paper web, said calender comprising: a roll system havinga plurality of rolls arranged to be in nip contact with each other, therolls forming a plurality of nips, through which a paper web to becalendered is arranged to pass, wherein at least the first or the lastcalendering nip of the multiple-nip calender is an extended nip; whereinthe extended nip is formed between one of said plurality of rolls whichis a polymer roll and a flexible hose shell arranged to rotate about aroll support, the shell being compressable against the polymer roll by acompression shoe mounted to the roll support.
 2. The multiple-nipcalender of claim 1 wherein each of the first and the last calenderingnip of the multiple-nip calender is an extended nip formed between oneof the plurality of rolls which is a polymer roll and a flexible hoseshell arranged to rotate about a roll support, the shell beingcompressible against the bottom roll by a compression shoe mounted tothe roll support.
 3. A supercalender for producing a matte-quality paperweb comprising: an upper roll which is a polymer roll and a bottom rollwhich is a polymer roll; at least one intermediate roll between theupper roll and the bottom roll, wherein each of the upper roll and thebottom roll form a nip with one of the at least one intermediate roll;and an extended nip engaged against at least one of the upper roll andthe bottom roll to define either the first or the last nip of thesupercalender, wherein the paper web to be calendered passes throughsaid extended nip and the nips formed with the at least one intermediateroll, wherein the extended nip is of the type formed by a flexible hoseshell arranged to rotate about a roll support, the shell beingcompressable against the at least one of the upper roll and the bottomroll by a compression shoe mounted to the roll support, or the extendednip is of the type formed by an endless flexible calendering beltarranged to be pressed against the at least one of the upper roll andthe bottom roll by a plurality of guide rolls which do not engage the atleast one of the upper roll and the bottom roll.
 4. The supercalender ofclaim 3 wherein both the upper roll and the bottom roll are engaged withan extended nip such that both the first and the last nip of thesupercalender are formed with extended nips.
 5. A multiple-nip calender,for producing a matte-quality paper web, said calender comprising: aroll system having a plurality of rolls arranged to be in nip contactwith each other, the rolls forming a plurality of nips, through which apaper web to be calendered is arranged to pass, wherein at least thefirst or the last calendering nip of the multiple-nip calender is anextended nip; and wherein the extended nip is formed between one of saidplurality of rolls which is a polymer roll and is an uppermost roll or alowermost roll, and an endless flexible calendering belt arranged to bepressed against the polymer roll with a plurality of guide rolls whichdo not engage any of said plurality of rolls.
 6. A method of producing aone-sided matte-quality paper web comprising the steps of: passing a webthrough an extended nip formed between a polymer roll which forms a toproll of a supercalender, and a flexible hose shell arranged to rotateabout a roll support, the shell being compressed against the top roll bya compression shoe mounted to the roll support; and passing the paperweb through each of a plurality of nips formed in the supercalender by aplurality of rolls, wherein the web after leaving the supercalender isthe one-sided matte-quality web.
 7. The method of claim 6 furthercomprising the step of passing the web through a second extended nipformed between a polymer roll which forms a bottom roll of thesupercalender, and a flexible hose shell arranged to rotate about a rollsupport, the shell being compressed against the bottom roll by acompression shoe mounted to the roll support.
 8. A method of producing aone-sided matte-quality paper web comprising the steps of: passing apaper web through each of a plurality of nips formed in a supercalenderby a plurality of rolls; and passing the web through an extended nipformed between a polymer roll which forms a bottom roll of thesupercalender, and a flexible hose shell arranged to rotate about a rollsupport, the shell being compressed against the bottom roll by acompression shoe mounted to the roll support, wherein the web afterleaving the extended nip is the one-sided matte-quality web.
 9. A methodof producing a one-sided matte-quality paper web comprising the stepsof: passing a web through an extended nip formed between a polymer rollwhich forms a top roll of a supercalender, and an endless flexiblecalendering belt arranged to be pressed against the polymer roll withthe aid of a plurality of guide rolls which do not engage the polymerroll; and passing the paper web through each of a plurality of nipsformed in the supercalender by a plurality of rolls, wherein the webafter leaving the supercalender is the one-sided matte-quality web. 10.The method of claim 9 further comprising the step of passing the webthrough a second extended nip formed between a polymer roll which formsa bottom roll of the supercalender, and an endless flexible calenderingbelt arranged to be pressed against the polymer roll with the aid of aplurality of guide rolls.
 11. A method of producing a one-sidedmatte-quality paper web comprising the steps of: passing a paper webthrough each of a plurality of nips formed in a supercalender by aplurality of rolls; and passing the web through an extended nip formedbetween a polymer roll which forms a bottom roll of the supercalender,and an endless flexible calendering belt arranged to be pressed againstthe polymer roll with the aid of a plurality of guide rolls which dosenot engage the polymer roll, wherein the web after leaving the extendednip is the one-sided matte-quality web.
 12. A method of producing aone-sided matte-quality paper web comprising the steps of: passing apaper web through each of a plurality of nips formed in a supercalenderby a plurality of rolls; and passing the web through an extended nipformed between a specially coated, heatable thermoroll which forms abottom roll or a top roll of the supercalender, and a flexible hoseshell arranged to rotate about a roll support, the shell beingcompressed against the bottom roll or the top roll by a compression shoemounted to the roll support, wherein the web after leaving the extendednip is the one-sided matte-quality web.
 13. A method of producing aone-sided matte-quality paper web comprising the steps of: passing apaper web through each of a plurality of nips formed in a supercalenderby a plurality of rolls; and passing the web through an extended nipformed between a polymer roll which forms a bottom roll or top roll ofthe supercalender, and a flexible hose shell arranged to rotate about aroll support, the shell being compressible against the polymer roll by acompression roll mounted for rotation wherein the web after leaving theextended nip is the one-sided matte-quality web.